Java預設方法

示例1

interface InterfaceA {
    default void say() {
        System.out.println("InterfaceA");
    }
}
public class DefaultMethod implements InterfaceA{
    public static void main(String[] args) {
        new DefaultMethod().say();
    }

}

輸出

InterfaceA

 示例2 實現類重寫default方法

interface InterfaceA {
    default void say() {
        System.out.println("InterfaceA");
    }
}
public class DefaultMethod implements InterfaceA{
    public void say() {
        System.out.println("DefaultMethod");
    }
    public static void main(String[] args) {
        new DefaultMethod().say();
    }

}

輸出

DefaultMethod

 示例3

interface InterfaceA {
    default void say(double m) {
        System.out.println("InterfaceA");
    }
}
public class DefaultMethod implements InterfaceA{
    public void say(int m) {
        System.out.println("DefaultMethod");
    }
    public static void main(String[] args) {
        DefaultMethod defaultMethod = new DefaultMethod();
        defaultMethod.say(1);
        defaultMethod.say(1L);
    }

}

輸出

DefaultMethod
InterfaceA

 示例4

interface InterfaceA {
    default void say() {
        System.out.println("InterfaceA");
    }
}
interface InterfaceAA extends InterfaceA{
    void say();
}
public class DefaultMethod implements InterfaceAA{
    public static void main(String[] args) {
        DefaultMethod defaultMethod = new DefaultMethod();
        defaultMethod.say();
    }
}

 輸出 報錯

示例5

interface InterfaceA {
    default void say() {
        System.out.println("InterfaceA");
    }
}
interface InterfaceAA extends InterfaceA{
    void say();
}
public class DefaultMethod implements InterfaceAA{
    public static void main(String[] args) {
        DefaultMethod defaultMethod = new DefaultMethod();
        defaultMethod.say();
    }

    @Override
    public void say() {
        System.out.println("defaultMethod");
        
    }
}

輸出

defaultMethod

 示例6

interface InterfaceA {
    default void say() {
        System.out.println("InterfaceA");
    }
}
interface InterfaceB {
    default void say() {
        System.out.println("InterfaceB");
    }
}
public class DefaultMethod implements InterfaceA,InterfaceB{
    public static void main(String[] args) {
        DefaultMethod defaultMethod = new DefaultMethod();
        defaultMethod.say();
    }
}

輸出 報錯

示例7

interface InterfaceA {
    default void say() {
        System.out.println("InterfaceA");
    }
}
interface InterfaceB {
    default void say() {
        System.out.println("InterfaceB");
    }
}
public class DefaultMethod implements InterfaceA,InterfaceB{
    public static void main(String[] args) {
        DefaultMethod defaultMethod = new DefaultMethod();
        defaultMethod.say();
    }
    @Override
    public void say() {
        InterfaceA.super.say();
        InterfaceB.super.say();
    }
}

輸出

InterfaceA
InterfaceB